Burn in Hours Charged against the Product Life Remaining
Accelerated burn in hours deduct directly from product life reserves based on activation energy kinetics and must be contractually capped to prevent premature field wear out.
Solder Joint Creep
Time-dependent Strain
Gradual and permanent deformation of a metal alloy when it is subjected to constant stress while held at high operating temperatures. Electronics manufacturers observe solder joint creep because most lead free alloys operate at a significant fraction of their melting point under typical load. This slow flow of metal eventually thins out connections or creates gaps that disconnect the circuit entirely.
Material Flow
Internal structures of the joint begin to shift as the grain boundaries slide under the influence of heat and pressure from board expansion. While dynamic impacts cause instant cracks, solder joint creep happens over months or years of steady heat exposure. The specific speed of this deformation varies according to the tin content and the grain refining additions in the solder paste.
Slower creep rates are generally preferred for components that will reside in high temperature server rooms or engine bays where thermal loads are consistent.
Failure Path
Eventually the accumulation of strain results in the formation of micro voids that link up to create a large rift. When the physical overlap between component lead and pad is lost, signal impedance rises sharply before the circuit fails completely. Knowledge of this process guides the choice of alloys for long term infrastructure.